amino acid, any of a group of organic molecules that consist of a basic amino group (−NH2), an acidic carboxyl group (−COOH), and an organic R group (or side chain) that is unique to each amino acid. The term amino acid is short for “α-amino [alpha-amino] carboxylic acid.” Each molecule contains a central carbon (C) atom, termed the α-carbon, to which both an amino and a carboxyl group are attached. The remaining two bonds of the α-carbon atom are generally satisfied by a hydrogen (H) atom and the R group. The formula of a general amino acid is: